Photoelectric conversion circuits are widely applied to optical communication modules. The transmission bandwidth of the optical communication modules is increased as the demand on data transmission is increased day by day. To meet the requirements of wide bandwidth transmission, the conversion circuit needs to maintain the loss in energy conversion as low as possible even when the transmission frequency is increased and a stable mechanical structure has to be provided such that the coupler of optical signals and electronic signals can carry out high efficient signal transmission.
FIG. 1 is a schematic diagram showing a conventional package framework for an optical communication module. As shown in FIG. 1, there has a driver chip 11 and a photoelectric element 12 disposed on a printed circuit board (PCB) 13. Bond wires are used between the photoelectric element 12 and the PCB 13 to accomplish the transmission of electronic signals therebetween. The bond wires are also used between the photoelectric element 12 and the driver chip 11 to accomplish the transmission of electronic signals therebetween. After the photoelectric element 12 converts the electronic signals into optical signals, the optical signals are transmitted to an optical fiber 15 via an optical prism 14, and then the optical fiber 15 carries the optical signals and transmits them to an external device. External optical signals carried by the optical fiber 15 can also be transmitted to the photoelectric element 12 via the optical prism 14, and then the photoelectric element 12 converts the optical signals into electronic signals.
In the optical communication module shown in FIG. 1, the bond wires are used between the photoelectric element 12 and the driver chip 11 or between the photoelectric element 12 and the PCB 13 to carry the transmission of electronic signals therebetween. However, the inductance of the bond wires limits the transmission bandwidth, and electromagnetic interference is occurred easily because of that. Further, the bond wires have a large variation during their manufacture processes, and therefore energy reflection and loss will be occurred in wide bandwidth transmission, thereby resulting in unable to increasing the data rate using the optical communication module. Further, because the photoelectric element 12 is mounted on the PCB 13, the transmission path of optical signals between the photoelectric element 12 and the optical fiber 15 has to be bent at an angle of 90 degrees. This is why the optical prism 14 is required. However, this increases the complexity of assembly and the manufacture cost.
FIG. 2 is a schematic diagram showing another conventional package framework for an optical communication module. The optical communication module shown in FIG. 2 adopts VCSEL/PD (Vertical-Cavity Surface-Emitting Laser/photodiode) as a photoelectric element 22. The photoelectric element 22 will produce a great deal of heat when it is running. Therefore, the photoelectric element 22 is generally connected to a carrier 24 via solder balls and then the carrier 24 is connected to a PCB 23 via a submount 27 such as a silicon optical bench (SiOB). However, the bond wires are still used to transmit the electronic signals between the driver chip 21 and the carrier 24 connected to the photoelectric element 22 or between the driver chip 21 and the processor chip 26 or other chips, and therefore the afore-mentioned problem of energy reflection and loss may still exist using the bond wires in wide bandwidth transmission. In addition, as to the example illustrated in FIG. 2, the optical signal transmission between the photoelectric element 22 and the optical fiber 25 uses an oblique surface formed on the submount 27 to change the path of optical signals. However, the volume of the submount 27 is quite large and it may affect the package density of the printed circuit board 23.
FIG. 3 is a signal characteristic diagram for the signals transmitted using a bond wire. The impedance of the bond wire is uncontrollable. When the frequency of signal is increased, the effect caused by impedance mismatch becomes more serious, and therefore the reflection coefficient (S11, solid line in FIG. 3) of the signals is increased as the frequency increases. This makes the energy all reflected from the input port to the signal source. In addition, resonance will occur at a specific frequency for the bond wire. This results in rapidly increasing insertion loss (S21, dash line in FIG. 3), and therefore the energy cannot be passed to the optical element by the driver circuit.
FIG. 4 is a schematic diagram showing a conventional package framework for a multichannel optical communication module. The multichannel optical communication module shown in FIG. 4 has two signal channels, for example. The channels have different transmission data. Each channel correspondingly has a TX optical element and a RX optical element. The TX optical element on the submount is connected to a corresponding TX junction point on the wafer by use of bond wire. The RX optical element on the submount is connected to a corresponding RX junction point on the wafer by use of bond wire. FIG. 4 merely illustrates the connections of the TX optical element and the RX optical element corresponding to a single channel. The corresponding connections for other channels are similar or the same. The conventional multichannel optical communication module with also uses the bond wires for electronic signal transmission. Said optical communication module generally has two or more than two TX and RX optical elements but the bond wires have not been shielded, and therefore coupling of the electronic signals will be occurred therebetween, resulting in abnormal signal transmission.
Further, please refer to FIG. 5, which is a spectrogram obtained at bond wires of a traditional photoelectric conversion circuit. The traditional photoelectric conversion circuit uses the bond wire for electronic signal transmission. However, the bond wire will generate strong radiation in high frequency signal transmission. This may also make the neighboring bond wire able to sense that energy and may cause maloperation of other integrated circuits. As shown in FIG. 5, the driver circuit at TX end is connected to the optical coupling element via the bond wire and TX end generates a strong electric field. RX end of the optical coupling element transmits the electronic signals to an amplifier circuit via the bond wire but meanwhile this bond wire will sense the energy from TX end due to electromagnetic coupling. This may cause maloperation of the circuits at RX end.